[PATCH v2] flow_dissector: prevent NULL pointer dereference in __skb_flow_dissect

[Anastasia Belova]

skb is an optional parameter, so it may be NULL.
Add check defore dereference in eth_hdr.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 690e36e726d0 ("net: Allow raw buffers to be passed into the flow dissector.")
Signed-off-by: Anastasia Belova <abelova@xxxxxxxxxxxxx>
---
 net/core/flow_dissector.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 272f09251343..68a8228ffae3 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1139,6 +1139,8 @@ bool __skb_flow_dissect(const struct net *net,
 
 	if (dissector_uses_key(flow_dissector,
 			       FLOW_DISSECTOR_KEY_ETH_ADDRS)) {
+		if (!skb)
+			goto out_bad;
 		struct ethhdr *eth = eth_hdr(skb);
 		struct flow_dissector_key_eth_addrs *key_eth_addrs;
 
-- 
2.30.2